Recycled method for a wasted polyester and reclaimed materials thereof

ABSTRACT

The present invention relates to a method for the recycling waste polyester resins and the reclaimed materials therefrom. The method for recycling waste polyester resins according to one embodiment the present invention comprises (a) depolymerizing waste polyester resin; (b) polycondensing the depolymerized product from step (a) with a polyhydric alcohol to provide a polyester polymer having an acid value of 10-150 mgKOH/g; and (c) recovering the polyester polymer in solid or liquid form if the polyester polymer from step (b) has an acid value of more than 20 mgKOH/g or recovering the polyester polymer in solid form if the polyester polymer from step (b) has an acid value of less than 20 mgkOH/g. The reclaimed polyester resin according to the present invention has the excellent compatibility, dispersibility, and adhesive property for various media, and can be used easily neutralized and dissolved in water. Accordingly, the polyester resin can be used as a useful material for industrial products.

TECHNICAL FIELD

(1) The present invention relates to a method for recycling wastepolyester resins and the reclaimed materials therefrom, and moreparticularly, to a recycling method for making liquid or solid polyesterresin compositions with excellent compatibility, solubility anddispersibility by depolymerizing and polycondensing crushed wastepolyester resins and the reclaimed materials therefrom.

BACKGROUND ART

(2) Polyester resins such as polyethylene terephthalate(hereinafterreferred to as “PET”) have good heat resistance, processability andtransparency, and non-toxicity compared with other materials, and,therefore are widely used for daily products and industrial supplies.Accordingly, a demand for polyester resins and production of that isincreasing continuously and the polyester resin wastes also increase. Asa result, environmental problems are looming large, concerning thetreatment of these wastes. These polyester resin wastes are specified asrecyclable in Korean Wastes Control Act but only a little amount of themis recycled, because the technological level of recycling method ismerely to remelt physically the waste polyester resins, and makeproducts and the quality of the reclaimed products is not satisfactory.Thus, treatment of the waste polyester resins becomes a serious problem,and methods for solving this problem are required desperately.

DISCLOSURE OF INVENTION

(3) Accordingly, the present invention is directed to a method forrecycling waste polyester resins and reclaimed materials therefrom thatsubstantially obviates one or more problems due to limitations anddisadvantages of the related art.

(4) An object of the present invention is to provide a recycling methodfor making liquid or solid polyester resins with excellentcompatibility, solubility and dispersibility by means ofdepolymerization and polycondensation of waste polyester resins.

(5) To achieve the object and in accordance with the purpose of theinvention, as embodied and broadly described herein, there is provided amethod for recycling waste polyester resins by depolymerizing andpolycondensing waste polyester resins. The method for recycling wastepolyester resins comprises:

(a) depolymerizing waste polyester resin;

(b) polycondensing the depolymerized product from step (a) with apolyhydric alcohol to provide a polyester polymer having an acid valueof 10-150 mg KOH/g; and

(c) recovering the polyester polymer in solid or liquid form if thepolyester polymer from step (b) has an acid value of more than 20 mgKOH/g or recovering the polyester polymer in solid form if the polyesterpolymer from step (b) has an acid value of less than 20 mg KOH/g.

BRIEF DESCRIPTION OF THE DRAWINGS

(6) Further objects and advantages of the invention can be more fullyunderstood from the following detailed description taken in conjunctionwith the accompanying drawings, in which:

FIG. 1 is a flow chart of a method for recycling waste polyester resinsin accordance with the present invention;

FIG. 2 is a flow chart of a method for recycling waste polyester resinsaccording to another embodiment of the present invention;

FIG. 3 is a flow chart of a method for recycling waste polyester resinsaccording to still another embodiment of the present invention.

FIG. 4 is a flow chart of a method for recycling waste polyester resinsaccording to still another embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

(7) Reference will now be made in detail to the preferred embodiments ofthe present invention, examples of which are illustrated in theaccompanying drawings.

FIG. 1 is a flow chart of a method for recycling waste polyester resinsin accordance with the present invention. As shown in FIG. 1, thecomposition of a reclaimed polyester resin in accordance with thepresent invention is produced through the steps comprising:

(a) depolymerizing waste polyester resin;

(b) polycondensing the depolymerized product from step (a) with apolyhydric alcohol to provide a polyester polymer having an acid valueof 10-150 mg KOH/g; and (c) recovering the polyester polymer in solid orliquid form if the polyester polymer from step (b) has an acid value ofmore than 20 mg KOH/g or recovering the polyester polymer in solid formif the polyester polymer from step (b) has an acid value of less than 20mg KOH/g.

The step (a) further comprises:

(a1) reacting the waste polyester resin with a solid resin dissolventfor primary depolymerization; and

(a2) reacting the depolymerized product from step (a1) with a polybasicacid for secondary depolymerization and an addition reaction.

(8) As the solid resin dissolvent to be used in the primarydepolymerization of step (a), one or more dissolvent can be selectedfrom the group of gum rosin, wood rosin, dehydrogenated rosin,hydrogenated rosin, maleic rosin, rosin ester, pinene resin, dipenteneresin, C5 petroleum resins, C9 petroleum resins, dammar resin, copalresin, dicyclopentadiene(hereinafter referred to as “DCPD”) resin,hydrogenated DCPD resin, and styrene maleic resin. The weight ratio ofwaste polyester resins to the solid resin dissolvent is 1:9-9:1. Inaddition, as the polybasic acid to be used in the secondarydepolymerization of step (a), one or more acids can be selected from thegroup of phthalic anhydride, isophthalic acid, terephthalic acid, adipicacid, azelaic acid, sebacic acid, tetrahydrophthalic anhydride, maleicanhydride, fumaric acid, itaconic acid, trimellitic acid, trimelliticanhydride, pyromellitic anhydride, succinic acid, cyclohexanedicarboxylic acid, naphthalene dicarboxylic acid, and benzoic acid. Theamount of polybasic acid to be used is 10˜70% by weight of the weight ofthe depolymerized product from step (a1).

(9) In the step (b), there is produced a polyester polymer having anacid value range of 10 to 150 mg KOH/g by polycondensing thedepolymerized product from step (a) with a polyhydric alcohol. Thepolyhydric alcohol, which adjust an acid value, to be used in the step(b) may be, for example, ethylene glycol, propylene glycol,1,3-propanediol, 1,3-butanediol, 1,6-hexanediol, neopentyl glycol,diethylene glycol, dipropylene glycol, polyethylene glycol, alkyleneoxide adduct of bisphenol A, trimethylol propane, glycerin,pentaerythritol, and a mixture thereof. The amount of the polyhydricalcohol to be used is 10˜70% by weight of the depolymerized product fromstep (a). The polyester polymer obtained via the step (a) and the step(b) is a solid resin. The weight average molecular weight of thepolyester polymer is 3,000-50,000 and the softening point is 70˜150° C.

(10) In the steps (a) and (b), the reactions are carried out in thepresence of 0.05˜0.5% by weight of the weight of depolymerization andpolycondensation catalysts at 200˜250° C.

(11) The step (c) has two different steps, i.e., a step for recoveringthe polyester polymer in solid or liquid form if the polyester polymerfrom the step (b) has an acid value of more than 20 mg KOH/g, or a stepfor recovering the polyester polymer in solid form if the polyesterpolymer from the step (b) has an acid value of less than 20 mg KOH/g.The polyester polymer in liquid form is produced by reacting thepolyester polymer from step (b) with a basic compound in order to obtaina neutralized polyester polymer and dissolving or dispersing theneutralized polyester polymer in water, a hydrophilic solvent, or amixture thereof.

(12) Here, as the basic compound to be used in the step (c) one or morecompounds can be selected from the group of sodium hydroxide, potassiumhydroxide, ammonium hydroxide, lithium hydroxide, and amines. The amountof the basic compound to be used is 3˜30% by weight of the polyesterpolymer from the step (b). In addition, as the hydrophilic solvent, oneor more solvents can be selected from the group of alcohols, ethers,acetone, diacetone alcohol, dimethyl formamide, tetrahydrofuran,ethylene glycol, propylene glycol, butylene, glycol, andN-methyl-2-pyrrolidone. The amount of the water, hydrophilic solvents,or a mixture of both of them to be added is 1˜10 times the weight of theneutralized polyester polymer.

(13) The resulted polyester resin is either a liquid or a solid state,and, when measured by means of a constant load capillary extrusionrheometer, the polyester resin has a flow beginning temperature (T_(fb))of 80˜105° C., a flow ending temperature (T_(end)) of 120˜160° C., and aglass transition temperature (Tg) of 40-80° C. Moreover, the polymerresin has excellent reactivity and dispersibility because it has two orthree carboxyl groups at the end of a polymer chain. The presentinvention can produce said polyester resin through recycling wastepolyester resins, and said raw materials may have various compositionratios.

(14) The present invention will be described in further detail withreference to the examples thereof, which examples however are merelyintended to be illustrative and not to be construed as limiting thescope of the invention.

EXAMPLE 1

The reclaimed polyester resin according to the present invention can beused as a toner binder for an electrophotograph and an electrostaticdevelopment.

The toner of the present invention is made of a polyester resin, acolorant, charge control agents and release agents by means ofpolymerization or crushing method. The colorant that can be selected isa black pigment such as carbon black and magnetite, a yellow pigmentsuch as iron oxide yellow, hansa yellow and permanent yellow, a bluepigment such as phthalocyanine blue and violet, a red pigment such asiron oxide red, carmine, toluidine red and quinacridone red, and a greenpigment such as phthalocyanine green and chrome green. The amount of thecolorant to be added is 1˜40 wt %. The charge control agents can beselected from the group of negrosin-based dyes and quaternary ammoniumsalts such as BONTRON N-07 and BONTRON N-21(available from OrientChemical Co., Ltd. (Japan)) as a plus(+) charge control agent, and azometal complex and salicylic acid metal complex such as BONTRON S-34) andBONTRON E-84(available from Orient Chemical Co., Ltd. (Japan)) as aminus(−) charge control agent. The amount of the charge control agent tobe used is 0.5˜5 wt % based on the amount of the binder resin. Therelease agent can be selected from the group of polyethylene wax,polypropylene wax, higher fatty acid esters, higher aliphatic alcohols.,carnauba wax and montan wax. One or more release agents can be used. Theamount of the release agent to be used is 0.5˜10 wt % based on theamount of the binder resin. To obtain an excellent image, theseadditives have to be well dispersed in the binder resin. The reclaimedpolyester resin of the present invention is well dispersed and dissolvedin water, hydrophilic solvents or a mixture thereof, and, therefore, atoner can be produced from polymerization method by dispersing saidadditives in the liquid polyester resin according to the presentinvention. In addition, in case of using crushing method, said additivescan be well dispersed in the solid polyester resin according to thepresent invention because the solid polyester resin has functional groupto play a role of a surfactant, and, therefore, it is possible toproduce a toner with a good performance. When measured by means of arheometer, the toner from Example 1 has a flow beginningtemperature(T_(fb)) of 80˜95° C. and a flow ending temperature (T_(end))of 120˜135° C. Moreover, the toner forms rapidly a very clear image, andhas desirable low temperature fixing and offset properties.

EXAMPLE 2

(15) The reclaimed polyester resin according to the present inventioncan be used as a composition of powder coating, which uses epoxy resinas a hardener. The polyester resin composition of the present inventionhas excellent reactivity and dispersibility because it has two or threecarboxyl groups at the end of polymer chains, and, therefore, by addinga little amount of anti-blocking agent to the polyester resin it canmaintain good storage stability. In addition, because the polyester isresin with a low softening temperature, the hardening reaction iscarried out in about ten minutes at less than 1.80° C. As a result, itis possible to lower the hardening temperature and to obtain highquality film of paint that has high gloss and excellent heat resistanceand chemical resistance.

EXAMPLE 3

(16) The reclaimed polyester resin according to the present inventioncan be used as a composition for oil modified alkyd varnish coatings andprinting inks. The solid polyester resin of the present invention reactswith fatty acid and drying oil, and the product therefrom can dissolvewell in aliphatic hydrocarbon solvents or aromatic hydrocarbon solvents,thereby providing a stable film of paint having excellent gloss, waterresistance and weatherability, and a high quality image. In gravureinks, the polyester resin of the present invention can provide a goodprinting image with high speed drying and excellent adhesive property,abrasion resistance and ruggedness, because it dissolves well in mixturesolvents of ketone solvents and aromatic hydrocarbon solvents.

EXAMPLE 4

(17) The reclaimed polyester resin according to the present inventioncan be used as a composition of an adhesive. The polyester resin of thepresent invention, which is used as a basic adhesive resin in a hotmeltadhesive, has a low softening temperature, a low melt viscosity, andexcellent adhesive property, water resistance, chemical resistance, andcompatibility. The hotmelt adhesive made of the polyester resin of thepresent invention provides excellent initial adhesive property andstrong adhesive force for paper, boards, leathers, fabrics, woods,plastics and metals such as aluminum. These adhesives can also be usedas liquid adhesives through dissolving them in various solvents.

(18) The said Examples will be described in further detail by referringto preparation examples, which examples however are merely intended tobe illustrative and not to be construed as limiting the scope of theinvention.

PREPARATION EXAMPLE 1

(19) Crushed waste PET chips (400 g), gum rosin (200 g) and monobutylstannoic acid (0.3 g) are placed in a reactor which is equipped with anagitator, a reflux condenser, a separator, a thermometer and a nitrogeninjection port. The mixture is heated to 250° C. and maintained over 2hours at that temperature. The mixture is agitated when the waste PETchips begin to be melted. After the mixture changes into a transparentstate, the reactor is cooled to 150° C., and then, maleic anhydride (180g) is added to the reactor. When the temperature of the mixture reachesto the point that ring-opening reaction is finished, the mixture isagain heated to 235° C. and maintained over 3 hours at that temperaturefor a depolymerization reaction. The acid value of the depolymerizationproduct is 115 mg KOH/g. Then, the reactor is charged with 200 grams ofethylene oxide adduct of bisphenol A. The reactor is heated to 250° C.and maintained over 5 hours at that temperature, and a polycondensationaccompanied with a dehydration reaction is carried out. When the acidvalue reaches to 55 mg KOH/g, the reactor is cooled and charged with 50grams of sodium hydroxide and 1,500 grams of per distilled water. Then,the mixture is stirred over 30 minutes at 85° C. The resultantwater-soluble polyester resin has an acid value of 39 mg KOH/g, a weightaverage molecular weight of 11,000, a softening point of 80° C. and pHof 8.5.

(20) Said water-soluble polyester resin can be used as a polymerizationtoner binder as follows. There are prepared the water-soluble polyesterresin (100 g), carbon black(3 g), charge control agents(0.1 g), andrelease agents(1 g). These reactants are mixed and dispersed, therebymaking suspended particles. The suspended particles are filtrated,washed by water, and dried to form a toner composition. Then, the driedtoner composition (100 g) is mixed with external additives (1 g), toproduce a toner. A toner cartridge filled with said toner can provide avery clear developed image. The toner produced from the reclaimedpolyester resin according to the present invention has excellentphysical properties and a fusing property.

PREPARATION EXAMPLE 2

(21) Crushed waste PET chips (400 g), hydrogenated rosin (200 g),monobutyl tartaric acid (0.3 g), trimellitic anhydride (150 g) andneopentyl glycol (200 g) are placed in a reactor which is equipped withan agitator, a reflux condenser, a separator, a thermometer and anitrogen injection port. The reaction method is the same withPreparation Example 1. The resultant water-soluble polyester resin hasan acid value of 30 mg KOH/g, a weight average molecular weight of12,000, a softening point of 95° C. and pH of 8.7.

(22) Said water-soluble polyester resin can be used as a polymerizationtoner binder as follows. There are prepared the water-soluble polyesterresin (10 g), carbon black (3 g), charge control agents (0.1 g), andrelease agents (1 g ). These reactants are mixed and dispersed, therebymaking suspended particles. The suspended particles are filtrated,washed by water, and dried to form a toner composition. Then, the driedtoner composition (100 g) is mixed with external additives (1 g ) toproduce a toner. A toner cartridge filled with said toner can provide avery clear developed image. The toner produced from the reclaimedpolyester resin according to the present invention has excellentphysical properties and a fusing property.

PREPARATION EXAMPLE 3

(23) Crushed waste PET chips (400 g), rosin ester (200 g), monobutylstannoic acid (0.3 g), fumaric acid (150 g), neopentyl glycol (100 g)and diethylene glycol (100 g) are placed in a reactor which is equippedwith an agitator, a reflux condenser, a separator, a thermometer and anitrogen injection port. The reaction method is the same withPreparation Example 1, except that potassium hydroxide (55 g) is used asa neutralizer instead of sodium hydroxide. The resultant water-solublepolyester resin has an acid value of 28 mg KOH/g, a weight averagemolecular weight of 12,000, a softening point of 105° C., and pH of 8.1.

PREPARATION EXAMPLE 4

(24) Crushed waste PET chips (400 g), C5 petroleum resins (200 g),monobutyl stannoic acid (0.3 g), trimellitic anhydride (150 g), ethyleneglycol (100 g) and trimethylol propane (80 g) are placed in a reactorwhich is equipped with an agitator, a reflux condenser, a separator, athermometer and a nitrogen injection port. The reaction method is thesame with Preparation Example 1, except that ammonium hydroxide (50 g)is used as a neutralizer instead of sodium hydroxide, and butyleneglycol (200 g) as a hydrophilic solvent instead of distilled water. Theresultant water-soluble polyester resin has an acid value of 30 mgKOH/g, a weight average molecular weight of 13,000, a softening point of108° C., and pH of 7.9.

PREPARATION EXAMPLE 5

(25) Crushed waste PET chips (400 g), C9 petroleum resins (200 g),monobutyl stannoic acid (0.3 g), adipic acid (50 g), maleic anhydride(100 g), propylene glycol (100 g) and neopentyl glycol (100 g) areplaced in a reactor which is equipped with an agitator, a refluxcondenser, a separator, a thermometer and a nitrogen injection port. Thereaction method is the same with Preparation Example 1, except thatsodium hydroxide (30 g) and trimethylamine (35 g) are used as aneutralizer instead of sodium hydroxide. The resultant water-solublepolyester resin has an acid- value of 31 mg KOH/g, a weight averagemolecular weight of 13,000, and pH of 7.7.

PREPARATION EXAMPLE 6

(26) Crushed waste PET chips (350 g), maleic gum rosin (250 g),monobutyl stannoic acid (0.3 g), trimellitic anhydride (100 g),neopentyl glycol (50 g), and ethylene oxide adduct of bisphenol A (150g) are placed in a reactor which is equipped with an agitator, a refluxcondenser, a separator, a thermometer and a nitrogen injection port. Thereaction method is the same with Preparation Example 1. The resultantwater-soluble polyester resin has an acid value of 45 mg KOH/g, a weightaverage molecular weight of 11,500, a softening point of 81° C., and pHof 8.7.

PREPARATION EXAMPLE 7

(27) Crushed waste PET chips (350 g), DCPD resin (250 g), monobutylstannoic acid (0.3 g), maleic anhydride (150 g), neopentyl glycol (100g) and polyethylene glycol (100 g) are placed in a reactor which isequipped with an agitator, a reflux condenser, a separator, athermometer and a nitrogen injection port. The reaction method is thesame with Preparation Example 1, except that ammonium hydroxide (030 g)and trimethylamine (50 g) is used as a neutralizer instead of sodiumhydroxide. The resultant water-soluble polyester resin has an acid valueof 30 mg KOH/g, a weight average molecular weight of 12,000, a softeningpoint of 95° C., and pH of 8.1.

PREPARATION EXAMPLE 8

(28) Crushed waste PET chips (400 g), DCPD resin (200 g), monobutylstannoic acid (0.3 g), isophthalic acid (100 g), adipic acid (50 g),neopentyl glycol (70 g) and ethylene oxide adduct of bisphenol A (120 g)are placed in a reactor which is equipped with an agitator, a refluxcondenser, a separator, a thermometer and a nitrogen injection port. Thereaction method is the same with Preparation Example 1, except thatneutralizing and solubilizing processes are skipped. The resultant solidpolyester resin has an acid value of 10 mg KOH/g, a weight averagemolecular weight of 20,000, and a softening point of 93° C.

PREPARATION EXAMPLE 9

(29) Crushed waste PET chips (500 g), gum rosin (200 g), monobutylstannoic acid(0.3 g), maleic anhydride(100 g) and pentaerythritol(200 g)are placed in a reactor which is equipped with an agitator, a refluxcondenser, a separator, a thermometer and a nitrogen injection port. Thereaction method is the same with Preparation Example 1, except thatneutralizing and solubilizing processes are skipped. The resultant solidpolyester resin has an acid value of 11 mg KOH/g, a weight averagemolecular weight of 30,000, and a softening point of 145° C.

(30) FIGS. 2-4 are flow charts of methods for recycling waste polyesterresins according to other embodiments of the present invention. Thefollowing Examples are being provided to further illustrate variousspecies of the present invention.

(31) EXAMPLE 5

As shown in FIG. 2, a composition of reclaimed polyester resin inaccordance with another embodiment of the present invention is producedthrough the phases comprising:

(a) reacting waste polyester resin with a polyhydric alcohol todepolymerize the waste polyester resin, removing excess polyhydricalcohol under reduced pressure, and reacting the reaction product with adepolymerization stabilizer solid resin to provide a stabledepolymerized product;

(b) addition-reacting the depolymerized product from step (a) with apolybasic acid and polycondensing the reaction product with a polyhydricalcohol to provide a polyester polymer having two or three carboxylicgroups at its chain end and having an acid value of 10˜150 mgKOH/g; and

(c) reacting the polyester polymer with a basic compound to provide aneutralized polyester polymer and dispersing the neutralized polyesterpolymer in water, a hydrophilic solvent, or a mixture thereof to providea dispersion of the polyester polymer.

(32) As the depolymerization stabilizer solid resin to be used in thestep (a), one or more materials can be selected from the group of rosin,rosin derivatives, hydrogenated rosin, rosin ester, dehydrogenatedrosin,maleic rosin, dammar resin, copal resin, petroleum resins, andderivatives of petroleum resins. The amount of the depolymerizationstabilizer solid resin to be used is 10˜100% by weight of thedepolymerized product. The polyhydric alcohol and polybasic acid to beused in the step (b) and the basic compound to be used in the step (c)are the same with the materials used at the making method of the presentinvention. The hydrophilic solvent to be used in the step (c) can beselected from the group of alcohols, acetone, diacetone alcohol,dimethyl formamide, dimethyl acetamide, ethyl cellosolve, butylcellosolve, tetrahydrofuran, and N-methyl-2-pyrrolidone. The amount ofthe hydrophilic solvent to be used is 10˜100% by weight of the polyesterpolymer from the step (b).

(33) The resultant polyester resin is either a liquid or a solid state,and has a flow beginning temperature (T_(fb)) of 80˜105° C., a flowending temperature (T_(end)) of 120˜160° C., and a glass transitiontemperature(T_(g)) of 40˜80° C.

(34) EXAMPLE 6

As shown in FIG. 3, a composition of reclaimed polyester resin inaccordance with another embodiment of the present invention is producedthrough the phases comprising:

(a) reacting waste polyester resin with a polyhydric alcohol todepolymerize the waste polyester resin, removing excess polyhydricalcohol under reduced pressure, and reacting the reaction product with adepolymerization stabilizer solid resin to provide a stabledepolymerized product;

(b) polycondensing the depolymerized product from step (a) with apolybasic acid, DMSSIP(dimethyl-5-sulfoisophthalate sodium salt), or amixture thereof and adding a polyhydric alcohol for use in adjustingacid value into the polycondensed product to provide a polyesterpolymer; and

(c) recovering the polyester polymer in liquid or solid form, whereinthe polyester polymer recovered in liquid form is dissolved in water, ahydrophilic solvent, or a mixture thereof.

The depolymerization stabilizer solid resin in the step (a), thepolyhydric alcohol and the polybasic acid in the step (b), and the basiccompound and the hydrophilic solvent in the step (c) are the same withthe materials used at the making method of the present invention. Inaddition, when the DMSSIP is mixed with the polybasic acid, the amountof DMSSIP to be used is 1-30% by weight of the total amount of thepolybasic acid.

(35) The resultant polyester resin is either a liquid or a solid state,and has a flow beginning temperature (T_(fb)) of 80˜105° C., a flowending temperature (T_(end)) of 120˜160° C., and a glass transitiontemperature (T_(g)) of 40˜80° C.

(36) EXAMPLE 7

As shown in FIG. 4, a composition of reclaimed polyester resin inaccordance with another embodiment of the present invention. is producedthrough the phases comprising.

(a) preparing a polyester resin having a residue of an sulfonic acidalkali metal salt of aromatic dicarboxylic acid includingDMSSIP(dimethyl-5-sulfoisophthalate sodium salt);

(b) reacting the polyester resin from step (a) with waste polyesterresin to depolymerize the waste polyester resin and polycondensing thereaction product to provide a polyester polymer, wherein thepolycondensation is accompanied by ester interchange reaction; and

(c) recovering the polyester polymer in liquid or solid form, whereinthe polyester polymer recovered in liquid form is dissolved in water, ahydrophilic solvent, or a mixture thereof.

The DMSSIP in the step (a) is one of sulfonic acid alkali metal salts ofaromatic dicarboxylic acids and functions as a compound causingdepolymerization. The mixture of the DMSSIP and a polybasic acid can beused instead of DMSSIP. Here, the amount of the mixture to be used isthe same with Example 6.

(37) The resultant polyester resin is either a liquid or a solid state,and has a flow beginning temperature (T_(fb)) of 80˜105° C., a flowending temperature (T_(end)) of 120˜160° C., and a glass transitiontemperature (T_(g)) of 40˜80° C.

Industrial Applicability

(38) The reclaimed polyester resin according to the present inventionhas the excellent compatibility, dispersibility, and adhesive propertyfor various media, and can be easily neutralized and dissolved in water.Accordingly, the polyester resin can be used as a useful material forindustrial products such as a developer for electrophotograph, ink-jetinks, a textile finishing agent, an adhesive, a binder of film coatings,a toner, a hotmelt adhesive, and a binder of powder coating.

1. A method for recycling waste polyester resin, the method comprising:(b) depolymerizing waste polyester resin; (b) polycondensing thedepolymerized product from step (a) with a polyhydric alcohol to providea polyester polymer having an acid value of 10-150 mgKOH/g; and (c)recovering the polyester polymer in solid or liquid form if thepolyester polymer from step (b) has an acid value of more than 20mgKOH/g or recovering the polyester polymer in solid form if thepolyester polymer from step (b) has an acid value of less than 20mgkOH/g.
 2. The method of claim 1, wherein step (a) comprises: (a1)reacting the waste polyester resin with a solid resin dissolvent forprimary depolymerization; and (a2) reacting the depolymerized productfrom step (a1) with a polybasic acid for secondary depolymerization andan addition reaction.
 3. The method of claim 2, wherein the solid resindissolvent is at least one selected from the group consisting of gumrosin, wood rosin, dehydrogenated rosin, hydrogenated rosin, maleicrosin, rosin ester, pinene resin, dipentene resin, C5 petroleum resins,C9 petroleum resins, dammar resin, copal resin, dicyclopentadiene resin,hydrogenerated dicyclopentadiene resin, and styrene maleic resin.
 4. Themethod of claim 2, wherein the weight ratio of the waste polyester resinto the solid resin dissolvent is in the range of 1:9˜9:1.
 5. The methodof claim 2, wherein the polybasic acid is at least one selected from thegroup consisting of phthalic anhydride, isophthalic acid, terephthalicacid, adipic acid, azelaic acid, sebacic acid, tetrahydrophthalicanhydride, maleic anhydride, fumaric acid, itaconic acid, trimelliticacid, trimellitic anhydride, pyromellitic anhydride, succinic acid,cyclohexane dicarboxylic acid, and naphthalene dicarboxylic acid.
 6. Themethod of claim 2, wherein the amount of the polybasic acid is in therange of 10˜70% by weight of the weight of the depolymerized productfrom step (a1).
 7. The method of claim 1, wherein steps (a) and (b) arecarried out in the presence of depolymerization and polycondensationcatalysts in an amount of 0.05˜0.5% by weight of the reactant.
 8. Themethod of claim 1, wherein steps (a) and (b) are carried out at atemperature of 200˜250° C.
 9. The method of claim 1, wherein thepolyhydric alcohol in step (b) is at least one selected from the groupconsisting of ethylene glycol, propylene glycol, 1,3-propanediol,1,3-butanediol, 1,6-hexanediol, neopentyl glycol, diethylene glycol,dipropylene glycol, polyethylene glycol, an alkylene oxide adduct ofbisphenol A, trimethylol propane, glycerin, and pentaerythritol.
 10. Themethod of claim 1, wherein the amount of the polyhydric alcohol in step(b) is in the range of 10˜70% by weight of the depolymerized productfrom step (a).
 11. The method of claim 1, wherein the polyester polymerin step (b) has a weight average molecular weight of 3,000˜50,000. 12.The method of claim 1, wherein the polyester polymer in step (b) has asoftening point of 70˜150° C.
 13. The method of claim 1, wherein step(c) of recovering the polyester polymer in liquid form comprises: (c1)reacting the polyester polymer from step (b) with a basic compound inorder to obtain a neutralized polyester polymer; and (c2) dissolving theneutralized polyester polymer from step (c1) in water, a hydrophilicsolvent, or a mixture thereof.
 14. The method of claim 13, wherein thebasic compound is at least one selected from the group consisting ofsodium hydroxide, potassium hydroxide, ammonium hydroxide, lithiumhydroxide, and amines.
 15. The method of claim 13, wherein the amount ofthe basic compound is in the range of 3˜30% by weight of the polyesterpolymer from step (b).
 16. The method of claim 13, wherein thehydrophilic solvent is at least one selected from the group consistingof alcohols, ethers, acetone, diacetone alcohol, dimethyl formamide,dimethyl acetamide tetrahydrofuran, ethylene glycol, propylene glycol,butylene glycol, and N-methyl-2-pyrrolidone.
 17. The method of claim 13,wherein the amount of water, the hydrophilic solvent, or the mixturethereof is in the range of 1˜10 times the weight of the neutralizedpolyester polymer.
 18. A method for recycling waste polyester resin, themethod comprising: (a) reacting waste polyester resin with a polyhydricalcohol to depolymerize the waste polyester resin, removing excesspolyhydric alcohol under reduced pressure, and reacting the reactionproduct with a depolymerization stabilizer solid resin to provide astable depolymerized product; (b) addition-reacting the depolymerizedproduct from step (a) with a polybasic acid and polycondensing thereaction product with a polyhydric alcohol to provide a polyesterpolymer having two or three carboxylic groups at its chain end andhaving an acid value of 10˜150 mgKOH/g; and (c) reacting the polyesterpolymer with a basic compound to provide a neutralized polyester polymerand dispersing the neutralized polyester polymer in water, a hydrophilicsolvent, or a mixture thereof to provide a dispersion of the polyesterpolymer.
 19. The method of claim 18, wherein the basic compound is atleast one selected from the group consisting of sodium hydroxide,potassium hydroxide, ammonium hydroxide, lithium hydroxide, and amines.20. The method of claim 18, wherein the amount of the basic compound isin the range of 3˜30% by weight of the polyester polymer from step (b).21. A method for recycling waste polyester resin, the method comprising:(a) reacting waste polyester resin with a polyhydric alcohol todepolymerize the waste polyester resin, removing excess polyhydricalcohol under reduced pressure, and reacting the reaction product with adepolymerization stabilizer solid resin to provide a stabledepolymerized product; (b) polycondensing the depolymerized product fromstep (a) with a polybasic acid, DMSSIP, or a mixture thereof and addinga polyhydric alcohol for use in adjusting acid value into thepolycondensed product to provide a polyester polymer; and (c) recoveringthe polyester polymer in liquid or solid form, wherein the polyesterpolymer recovered in liquid form is dissolved in water, a hydrophilicsolvent, or a mixture thereof.
 22. The method of claim 18 or 21, whereinthe depolymerization stabilizer solid resin is at least one selectedfrom the group consisting of rosin and derivatives thereof, hydrogenatedrosin, rosin ester, dehydrogenated rosin, maleic rosin, dammar resin,copal resin, petroleum resin and derivatives thereof.
 23. The method ofclaim 18 or 21, wherein the amount of the depolymerization stabilizersolid resin is in the range of 10˜100% by weight of the depolymerizedproduct.
 24. The method of claim 18 or 21, wherein the polyhydricalcohol is at least one selected from the group consisting of ethyleneglycol, propylene glycol, 1,3-propanediol, 1,3-butanediol,1,6-hexanediol, neopentyl glycol, diethylene glycol, dipropylene glycol,polyethylene glycol, an alkylene oxide adduct of bisphenol A,trimethylol propane, glycerin, and pentaerythritol.
 25. The method ofclaim 18 or 21, wherein the polybasic acid is at least one selected fromthe group consisting of phthalic anhydride, isophthalic acid,terephthalic acid, adipic acid, azelaic acid, sebacic acid,tetrahydrophthalic anhydride, maleic anhydride, fumaric acid, itaconicacid, trimellitic acid, trimellitic anhydride, pyromellitic anhydride,succinic acid, cyclohexane dicarboxylic acid, and naphthalenedicarboxylic acid.
 26. The method of claim 18 or 21, wherein the amountof the polybasic acid is in the range of 10˜50% by weight of thedepolymerized product from step (a).
 27. A method for recycling wastepolyester resin, the method comprising: (a) preparing a polyester resinhaving a residue of an sulfonic acid alkali metal salt of aromaticdicarboxylic acid including DMSSIP; (b) reacting the polyester resinfrom step (a) with waste polyester resin to depolymerize the wastepolyester resin and polycondensing the reaction product to provide apolyester polymer, wherein the polycondensation is accompanied by esterinterchange reaction; and (c) recovering the polyester polymer in liquidor solid form, wherein the polyester polymer recovered in liquid form isdissolved in water, a hydrophilic solvent, or a mixture thereof.
 28. Themethod of claim 21 or 27, wherein the amount of DMSSIP is in the rangeof 1˜30% by weight of a polybasic acid when used along with thepolybasic acid.
 29. The method of claim 18, 21, or 27, wherein thehydrophilic solvent is at least one selected from the group consistingof alcohols, acetone, diacetone alcohol, dimethyl formamide, dimethylacetamide, ethylcellosolve, butylcellosolve, tetrahydrofuran, andN-methyl-2-pyrrolidone.
 30. The method of claim 18, 21, or 27, whereinthe amount of the hydrophilic solvent is in the range of 10˜100% byweight of the polyester polymer from step (b).
 31. A polyester resin insolid or liquid form recovered by the method of any one of claims 1, 18,21, or
 27. 32. The polyester resin of claim 31, having a flow beginningtemperature T_(fb) of 80˜105° C.
 33. The polyester resin of claim 31,having a flow end temperature T_(end) of 120˜160° C.
 34. The polyesterresin of claim 31, having a glass transition temperature T_(g) of 40˜80°C.
 35. The polyester resin of claim 31, being used as one of a developerfor electrophotography, ink-jet ink, a textile finishing agent, anadhesive, a film coating binder, a toner, a hotmelt adhesive, and apowder coating binder.